Recently, personal computers have included Optical Disk Drives as well as Hard Disk Drives as standard equipment. At one time, the majority of optical disk drives were CD-ROM. Now DVD-ROM drives, and/or CD-R/CD-RW drives have become standard equipment. Further, DVD-R drives, DVD-RAM drives and DVD-ROM/CD-ROM drives have appeared in the market, and progress has been made in the design of optical disk drives within even higher performance and features.
FIG. 5 shows an example of an optical disk device for driving an optical disk such as a CD-ROM and a CD-RW. This optical disk drive is under control of Central Processing Unit (CPU) 21. Driver 17 controls drive rotation of spindle motor 12 and the motor 12 rotates an optical disk 11 at a constant linear velocity or a constant angular velocity. A laser beam is irradiated on a surface of the rotating optical disk 11 by optical pickup 13, moving radially from the inner circumference side to the outer circumference side of the disk 11. On the surface of the disk 11, data is recorded in a spiral by a recess called a pit where existence of the pit changes reflection quantity of laser beam. The optical pickup 13 reads data on the optical disk 11 by the change in reflection quantity of the laser beam.
Data read from the optical disk 11 is waveshaped by an analog front end 18. Signal processing (such as error correction and so on) is then performed by a digital signal processor 19. Data is then transferred to an external host 22 through decoder 20.
In order to read data correctly, the CPU 21 commands the driver 17 to perform focus control for focusing a laser beam on the optical disk 11, and tracking control for positioning a laser beam on a center of a track, based on output signal from the digital signal processor 19. Focus control is performed by driver 17 driving a lens 14, which is supported by wire in a housing of the optical pickup 13, perpendicularly to the surface of the optical disk 11. Tracking control is performed by the driver 17 driving the lens 14 in a horizontal direction radially to the surface of the optical disk 11 based on a gap between the center of the radiated laser beam spot and the center of the track detected by CPU 21 through a change in reflection quantity of the laser beam from the optical disk 11.
As described above, data is recorded in a spiral (this is generally called a track). Therefore, when reading data, the optical pickup 13 moves from the inner circumference of the disk to outer circumference side of the disk as time passes. Optical pickup 13 is moved through two kinds of movement. One kind of movement includes moving the lens 14 within the housing of the optical pickup 13. Another kind of movement includes moving the feed 15 to which the optical pickup 13 is fixed. Normally, the lens 14 moves within the housing of the optical pickup 13 at first to follow the track until the lens 14 moves a certain distance away from the center of the housing, and then the feed 15 moves so that the lens 14 returns to the center of the housing. The feed 15 is controlled by feed motor 16 which is under control of CPU 21 through the driver 17.
When reading data of an arbitrary position on the surface of the optical disk 11 based on a command from external device etc., a seek operation is performed. The seek operation includes moving the optical pickup 13 across track(s) from a present track to a target track where desired data is recorded. Movement of optical pickup 13 is accomplished through two kinds of operations. A seek operation of moving the feed 15 to carry the optical pickup 13 to a target track is called feed seek, and is used for comparatively long distance movement. On the other hand, moving the lens 14 within the housing of the optical pickup 13 to the target track without moving the feed 15 is called kick seek, and is used for comparatively short distance movement. Seek operation is performed by combining these two kinds of seek operations.
A control method of the feed 15 in feed seek operation is now described. CPU 21 searches the number of tracks from a present track to a target track and commands the driver 17 to move the optical pickup 13 across the number of tracks corresponding to the number searched. The driver 17 drives the feed motor 16 to control the drive of the feed 15 based on the command.
This command commands a feed control amount, which includes maximum speed in a constant-speed region, acceleration in an acceleration region, and acceleration in a deceleration region, in order to control drive of the feed 15. The feed control amount is provided based on a standard acceleration/deceleration control algorithm (hereinafter called standard control algorithm), which is stored in internal memory of CPU 21 or external memory 23 in advance. This standard control algorithm is created based on speed characteristics of the feed 15 (shown in FIG. 6) acquired by actually moving the optical pickup 13 from a certain location to a desired location in standard control algorithm setting stage. This speed characteristic of the feed 15 consists of acceleration region 61, constant-speed region 62 and deceleration region 63 as shown in FIG. 6. This standard control algorithm is to acquire standard setting for the feed 15 performances and set at product shipment. It is also called seek profile.
However, because of size dispersion of mechanical parts used for the feed 15, quality variation of the grease used, or size and characteristic change due to temperature variation and so on, a load applied to the feed motor 16 for moving the feed 15 in startup (hereinafter called starting load) can change from that in the setting stage. In that case, even if the feed control amount based on the standard control algorithm is given to the driver 17, speed characteristics of the setting stage as shown in FIG. 6 cannot be obtained, or there is a possibility that the optical pickup 13 cannot reach to the target track or overshoot. FIG. 7 and FIG. 8 show examples illustrating that there are problems in speed characteristics. When the starting load is heavier, problems such as the target speed cannot be achieved in acceleration (as shown by line 71) or stalling before the target track when decelerating (as shown by line 72) occur. On the other hand, when the starting load is lighter, acceleration is too great and problems such as the speed exceeding the setting speed in acceleration (as shown by line 81) or that the optical pickup cannot stop at the target track because enough deceleration is not achieved and overshoots in deceleration (as shown by line 82) occur. In other words, the starting load is based on the mechanical resistance applied on the feed motor 16 when moving the feed 15.